The field of the invention is generally that of alarm apparatuses or warning devices or equipment capable of indicating the presence of some predetermined condition or object so that a person's attention, which might otherwise be occupied with other matters, will be immediately alerted to the presence of said condition or object for use in a decision-making process as to what action, if any, the person will take, based upon his recognition of the presence of the condition or object. More particularly, the present invention pertains to apparatus intended to solve the prior art problem of providing to the driver of a first vehicle (and all other similar relatively close vehicles which are intended to be warned) immediate awareness of the presence of a nearby second vehicle, such as an emergency vehicle or the like, which usually is provided with an emergency vehicle siren for this purpose, but which may not be heard if the driver of the first vehicle has its windows closed and/or has entertainment equipment within his vehicle operating, especially if it is operating so as to produce a loud output sound which may completely mask the siren sound coming from the nearby emergency vehicle, so that the driver of the first vehicle will not be aware of its presence. This is an extremely dangerous situation since such an emergency vehicle producing such a warning signal sound may be travelling very rapidly and if the driver of the first motor vehicle is unaware of its presence, he will not take proper evasive action and his vehicle may be struck by the rapidly-approaching emergency vehicle, which may cause an extremely serious accident which may result in injury or possible death. It is believed to be evident that the provision of a warning-signal-producing apparatus which would completely meet and overcome the above prior art problem by positively alerting the driver of such a vehicle of the presence of such a nearby emergency vehicle would be extremely desirable, and it is precisely this desirable objective, and the overcoming of the above-mentioned prior art disadvantages, which are obtained in and through the use of the novel apparatus of the present invention by reason of the novel features thereof, as set forth hereinafter.